I've just had an unexpected failure of my 6 year old sump pump, resulting in
a fair amount of rain water in my basement.

In considering replacements, the thought occurs to me that a 2nd redundant
pump placed above the replacement primary pump would hopefully prevent this
situation from occurring again.

The sump is 18 inches in diameter and 28 inches deep, enough space (I think)
to mount two pumps, one above the other.

I am a bit uncertain as to how, if at all, I should use one-way valves in
the discharge plumbing to prevent backflow.

The discharge line is 1-1/4inch NPT. I am wondering if just using a "tee" to
join the two discharge lines would be sufficient?

Any thoughts would be most appreciated and thank you in advance.

Happy Thanksgiving to a terrific group of very knowledgeable and helpful
people!

Smarty